In a variety of manufacturing processes, it is necessary to grip or hold a workpiece and/or component to enable an operation or work to be performed on the workpiece or component. For example, one such operation is stretch forming which employs a stretch-wrap machine or the like.
Stretch forming is a process for forming contoured metal parts or workpieces by pulling and wrapping extrusions around a die. During the stretch forming process, the workpiece is typically gripped at opposite ends using a pair of gripping devices of the stretch-wrap machine. The gripping devices are then moved apart to apply tension to the workpiece. The tensioned workpiece is then bent around a forming member or die to form a desired shape.
During the stretch forming process, the stress on the workpiece becomes so great that the metal reaches a state of semi-plasticity. This occurs by stretching the workpiece beyond its yield point. Metal structures undergoing such deformation, upon release of the tension, remain permanently deformed. This permanent deformation of the metal causes the workpiece to remain the desired shape into which it was formed during the stretch wrap process.
One approach currently employed for gripping and holding a workpiece for stretch forming, is to fabricate a set of complementary jaws that correspond to each configuration of workpiece that is to be gripped. Typically, several jaw insert segments collectively make what is referred to as the jaw insert. These insert segments are placed into a housing or sleeve, generally known as a jaw head or insert chamber, and fit together and define at their adjoining, axially-extending surfaces a profile, i.e., the cross-section, of the workpiece to be stretch formed. In the above-described gripping device and method, the jaw inserts must be precisely manufactured to a relatively exact shape which compliments that of the workpiece, in order to enable the jaw head and jaw inserts to function properly. Therefore, as a consequence, each unique configuration of each workpiece to be gripped and subsequently stretched, requires its own set of dedicated jaw inserts.
Thus, the aforementioned approach to stretch forming has drawbacks. Whenever a workpiece having a different profile is to be formed, the jaw inserts must be changed. Also, if a substantial number of different workpiece configurations or profiles are to be worked on, it can become quite expensive to fabricate and maintain the required inventory of jaw insert sets. Moreover, the changing of jaw inserts in response to different profiles of workpieces requires that the jaw head or gripper assembly be disassembled and removed by the operator. The aforementioned disassembly and removal can be very laborious and fatiguing considering the gripper assemblies can be very heavy, oftentimes weighing 120 lbs or more. Also, the exchanging of jaw inserts can be very time consuming, causing the manufacturing process to be inefficient to some extent.
Another approach for gripping a workpiece that is currently employed in the art is to install a “gripper jaw” in the jaw portion of the stretch former that has a shape that is generally complementary to that of the workpiece. In this approach, the workpiece is subsequently modified in shape in the area to be gripped to match the shape of the gripper jaw. This approach, however, has drawbacks also, because it adds considerable time to the manufacturing process for the workpiece while it also requires modifications to the workpiece in many instances that are oftentimes undesirable. In some instances, the requisite modifications to the workpiece may result in the modifications being transferred to other areas of the workpiece during manufacturing operations, causing the workpiece to become flawed.
Accordingly, there is a need in the art to provide an apparatus and method that allows for the efficient manufacture of workpieces having various configurations, using stretch forming processes and the like. Further, there is a need in the art that allows for the ease of removal or exchange of jaw inserts of a jaw head or the like, that is ergonomic and less fatiguing.